Subsequent events (Details) - Sebree, Kentucky [Member] - Subsequent Event [Member]	Oct. 30, 2015 potline
Subsequent Event [Line Items]
Curtailment notice, number of intended potline closings	1
Number of potlines	3

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

No definition available.

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration